How to add sets?

Question

I have two sets set([1,2,3] and set([4,5,6]. I want to add them in order to get set 1,2,3,4,5,6.

I tried:

b = set([1,2,3]).add(set([4,5,6]))

but it gives me this error:

Traceback (most recent call last):

  File "<ipython-input-27-d2646d891a38>", line 1, in <module>
    b = set([1,2,3]).add(set([4,5,6]))

TypeError: unhashable type: 'set'

Question: How to correct my code?

Does this answer your question? [How do I add two sets](https://stackoverflow.com/questions/29648520/how-do-i-add-two-sets) — AMC, Mar 10 '20 at 01:09

Mark · Accepted Answer · 2020-03-09T23:50:22.413

2

You can take the union of sets with |

> set([1, 2, 4]) | set([5, 6, 7])
{1, 2, 4, 5, 6, 7}

Trying to use add(set([4,5,6])) is not working because it tries to add the entire set as a single element rather than the elements in the set — and since it's not hashable, it fails.

edited Mar 09 '20 at 23:50

answered Mar 09 '20 at 23:24

Mark

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sorry for being pedantic but I think `a.union(b)` is cleaner. – Charlie Parker Aug 12 '21 at 15:36
I don't think that's pedantic @CharlieParker, just an opinion. `a.union(b)` is nice, so is `a | b`. Both loose a little luster when you solve the *actual* problem and write something like: `set([1, 2, 4]).union([5, 6, 7])` or set variables `a` and `b` first to give that nice, clean feel as @khuynh did below. – Mark Aug 12 '21 at 16:03
perhaps the reason I think it's pedantic is that `|` is usually used for Ors - for booleans. Yes it is isomorphic sort of to set union but the Or of a set doesn't really exist. What exists is the union of them. That's what I meant. – Charlie Parker Aug 15 '21 at 16:37
'or' makes perfect sense here and the relationship between `or -> union` and `and -> intersection` is [common in the math literature](https://eng.libretexts.org/Bookshelves/Computer_Science/Programming_and_Computation_Fundamentals/Foundations_of_Computation_(Critchlow_and_Eck)/02%3A_Sets_Functions_and_Relations/2.02%3A_The_Boolean_Algebra_of_Sets). A union represents items in set A **or** set B. An intersection represents items in set A **and** set B. This is reflected in the choice of `|` and `&` for these operators. – Mark Aug 15 '21 at 16:46

kennyvh · Answer 2 · 2020-03-09T23:45:35.883

1

You should use the union operation with the .union method or the | operator:

>>> a = set([1, 2, 3])
>>> b = set([4, 5, 3])
>>> c = a.union(b)
>>> print(c)
{1, 2, 3, 4, 5}
>>> d = a | b
>>> print(d)
{1, 2, 3, 4, 5}

See the complete list of operations for set.

edited Mar 09 '20 at 23:45

answered Mar 09 '20 at 23:24

kennyvh

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How to add sets?

2 Answers2